Hydraulic pilot operated directional control valve

ABSTRACT

A hydraulic pilot operated directional control valve (30; 60; 70) in which at least one pilot hydraulic pressure chamber (40, 41; 76) is formed within a block (39; 64; 75) of a hydraulic pilot operating section (32, 33; 61; 72), and pilot hydraulic fluid is led into the pilot hydraulic pressure chamber to drive a spool (37, 38; 74). A drain passageway (54; 82) is provided in the vicinity of the pilot hydraulic pressure chamber (40, 41; 76) within the block (39; 64; 75), and the pilot hydraulic pressure chamber and the drain passageway communicate with each other through minute passageway means (52, 53; 83) for bleeding air.

TECHNICAL FIELD

The present invention relates to hydraulic pilot operated directionalcontrol valves and, in particular, to a hydraulic pilot operateddirectional control valve which is controlled in a manner switched inresponse to a pilot pressure, for controlling flow of hydraulic fluidsupplied to hydraulic actuators in hydraulic machines such as ahydraulic excavator and the like.

BACKGROUND ART

Hitherto, a hydraulic pilot operated directional control valve haswidely been used to control flow of hydraulic fluid supplied tohydraulic actuators in a hydraulic machine such as a hydraulic excavatoror the like, to control motion of the hydraulic actuators.

FIG. 1 shows a hydraulic circuit having incorporated therein suchhydraulic pilot operated directional control valve. In the figure, thereference numeral 1 denotes the hydraulic pilot operated directionalcontrol valve which is composed of a valve body section 2 and hydraulicpilot operating sections 3 and 4. The valve body section 2 is connectedto a hydraulic pressure source 5 and a reservoir 6, and is connected toa hydraulic actuator 7, for controlling flow of hydraulic fluid suppliedfrom the hydraulic pressure source 5 to the hydraulic actuator 7. Theoperating sections 3 and 4 are connected to a pilot valve 10 throughrespective pilot lines 8 and 9. The pilot valve 10 is adapted togenerate a pilot pressure for controlling operation of the valve bodysection 2. The reference numeral 11 denotes a pilot hydraulic pressuresource for the pilot valve 10.

Usually, the directional control valve 1 is formed into a multi-spoolvalve having accommodated therein a plurality of spools. The directionalcontrol valve 1 has connected thereto pilot valves and pilot linescorresponding in number to the spools. FIG. 1, however, shows only thehydraulic actuator 7 and a pilot circuit 8, 9, 10 with respect to one ofthe valve elements, for convenience of illustration.

As shown in FIG. 2, the directional control valve 1 has a plurality ofspools 13 and 14 which are accommodated, for sealing movement, in ablock 12 of the valve body section 2. The directional control valve 1also has a plurality of pilot hydraulic pressure chambers 16 and 17which are formed in a block 15 of the operating section 3 in a mannercorresponding respectively to the plurality of spools 13 and 14.

Various grooves for controlling flow of the hydraulic fluid are formedin outer peripheral surfaces of the respective spools 13 and 14 and inopposed inner peripheral surfaces of the block 12. Of these grooves,FIG. 2 shows only drain grooves 18 through 21. The grooves 20 and 21 inthe block 12 are connected to the reservoir 6 so that the hydraulicfluid is returned to the reservoir 6 through the grooves 20 and 21.

The pilot hydraulic pressure chambers 16 and 17 have accommodatedrespectively therein springs 22 and 23 for applying return forcesrespectively to the spools 13 and 14. Adapters 26 and 27 having thereinrespective pilot ports 24 and 25 are mounted to the block 15 throughrespective threadedly engaging portions 28 and 29. The pilot pressure isintroduced into the pilot hydraulic pressure chambers 16 and 17 throughthe respective pilot ports 24 and 25. The adapter 26 is connected to thepilot valve 10 through the pilot line 8, while he adapter 27 isconnected to a pilot line and a pilot valve which are not shown.

Although not shown, the hydraulic pilot operating section 4 isconstructed in a manner similar to the operating section 3.

In this hydraulic pilot operated directional control valve 1, as thepilot valve 10 is operated, the pilot pressure is led from the pilotport 24 of the adapter 26 into the pilot hydraulic pressure chamber 16through one of the pilot lines 8 and 9, for example, the pilot line 8,depending upon the direction in which the pilot valve 10 is operated. Bythis pilot pressure, the spool 13 is moved downwardly as viewed in thefigure, to cause the hydraulic fluid from the hydraulic pressure source5 to be supplied to the hydraulic actuator 7 through a plurality ofgrooves, not shown, formed in the spool 13 and the block 12, therebydriving the actuator 7. The returning hydraulic fluid from the hydraulicactuator 7 is returned to the reservoir 6 through the grooves 18 and 20.

By the way, in the hydraulic pilot operated directional control valve 1constructed in this manner, air mingled in the pilot hydraulic fluidmight be accumulated within the pilot hydraulic pressure chambers 16 and17. If air is accumulated within the pilot hydraulic pressure chambers16 and 17, switching speed, that is, responsibility of the hydraulicpilot operated directional control valve 1 with respect to the pilotpressure is deteriorated. Accordingly, in such case, so-called airbleeding is carried out in such a manner that the adapters 26 and 27 aredetached from the block 15 to release air within the pilot hydraulicpressure chambers 16 and 17 to the outside.

However, operation of manually attaching and detaching the adapters 26and 27 is considerably troublesome. In particular, it has taken time toremove oil adhering to the adapters 26 and 27 and the like. Moreover,even if the air bleeding has once been carried out, similar air bleedinghas again been required to be effected after the elapse of apredetermined period of time, thus involving the maintenance cost.

It is therefore an object of the invention to provide a hydraulic pilotoperated directional control valve in which release of air accumulatedwithin a pilot hydraulic pressure chamber to the outside can be carriedout automatically without the need of manual operation.

DISCLOSURE OF THE INVENTION

In a hydraulic pilot operated directional control valve in which atleast one pilot chamber is formed within a block of a hydraulic pilotoperating section, and pilot hydraulic fluid is introduced into thepilot chamber to drive a spool, the hydraulic pilot operated directionalcontrol valve of the invention is characterized in that a drainpassageway is provided in the vicinity of the pilot hydraulic pressurechamber within said block, and the pilot hydraulic pressure chamber andthe drain passageway communicate with each other through minutepassageway means for bleeding air.

With such arrangement, air accumulated within the pilot hydraulicpressure chamber is released into a reservoir through the minutepassageway means and the drain passageway, so that air bleeding isautomatically carried out.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a hydraulic circuit in which aconventional hydraulic pilot operated directional control valve isincorporated;

FIG. 2 is a cross-sectional view of a principal portion of the hydraulicpilot operated directional control valve;

FIG. 3 is a circuit diagram showing a hydraulic circuit in which ahydraulic pilot operated directional control valve according to anembodiment of the invention is incorporated;

FIG. 4 is a cross-sectional view of a principal portion of the hydraulicpilot operated directional control valve;

FIG. 5 is a cross-sectional view of a principal portion of a hydraulicpilot operated directional control valve according to another embodimentof the invention; and

FIG. 6 is a cross-sectional view of a principal portion of a hydraulicpilot operated directional control valve according to still anotherembodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the invention will be described below with reference toFIGS. 3 through 6.

In FIG. 3, the reference numeral 30 denotes a hydraulic pilot operateddirectional control valve according to an embodiment of the invention.The control valve 30 is composed of a valve body section 31 andhydraulic pilot operating sections 32 and 33. In FIG. 3, like referencenumerals are used to designate component parts like those illustrated inFIG. 1. That is, the valve body section 31 is connected to a hydraulicpressure source 5 and a reservoir 6, and is connected to a hydraulicactuator 7, for controlling flow of hydraulic fluid supplied from thehydraulic pressure source 5 to the hydraulic actuator 7. The operatingsections 32 and 33 are connected to a pilot valve 10 through respectivepilot lines 8 and 9. The pilot valve 10 is adapted to generate pilotpressure for controlling operation of the valve body section 31. Theoperating sections 32 and 33 are also connected to the reservoir 6through respective drain lines 34 and 35 for the purposes subsequentlyto be described. the reference numeral 11 denotes a pilot hydraulicpressure source for the pilot valve 10.

The directional control valve 30 is preferably formed into a multi-spoolvalve having accommodated therein a plurality of spools. The directionalcontrol valve 30 has connected thereto pilot valves and pilot linescorresponding in number to the spools. FIG. 3, however, shows only thehydraulic actuator 7 and a pilot circuit 8, 9, 10 with respect to one ofthe valve elements, for convenience of illustration.

As shown in FIG. 4, the directional control valve 30 has a plurality ofspools 37 and 38 which are accommodated, for sealing movement, within ablock 36 of the valve body section 31. The directional control valve 30also has a plurality of pilot hydraulic pressure chambers 40 and 41formed within a block 39 of the operating section 32 in a mannercorresponding respectively to the plurality of spools 37 and 38.

Various grooves for controlling flow of the hydraulic fluid are formedin outer peripheral surfaces of the respective spools 37 and 38 and inopposed inner peripheral surfaces of the block 36. Of the grooves, FIG.4 shows only drain grooves 42 through 45. The grooves 44 and 45 in theblock 36 are connected to the reservoir 6 so that the hydraulic fluid isreturned to the reservoir 6 through the grooves 44 and 45.

Accommodated respectively in the pilot hydraulic pressure chambers 40and 41 are springs 46 and 47 for applying return forces respectively tothe spools 37 and 38. Adapters 50 and 51 having therein respective pilotports 48 and 49 are mounted to the block 39. The pilot pressure isintroduced into the pilot hydraulic pressure chambers 40 and 41 throughthe respective pilot ports 48 and 49. The adapters 50 and 51 aredetachably mounted to the block 39 through respective threadedlyengaging portions 52 and 53 which are constituted respectively bythreaded engagement of male threads formed on the adapters with femalethreads formed in the block 39.

A drain passageway 54 independent of the drain grooves 44 and 45 formedin the block 36 of the valve body section 31 is provided in the vicinityof the pilot hydraulic pressure chambers 40 and 41 within the block 39.The drain passageway 54 is connected to the reservoir 6 through theabove-mentioned drain line 34.

The aforesaid threadedly engaging portions 52 and 53 are located fromthe respective pilot hydraulic pressure chambers 40 and 41 to the drainpassageway 54. The pilot hydraulic pressure chambers 40 and 41communicate with the drain passageway 54 through respective gaps at thethreadedly engaging portions 52 and 53. The gaps at the respectivethreadedly engaging portions 52 and 53 have their respectivecross-sectional flow passage areas of the order that enables passage ofair, but almost prevents passage of the pilot hydraulic fluid. Thus, thegaps constitute minute passageway means for bleeding air.

Although not shown, the operating section 33 is likewise constructed.

In the embodiment constructed in this manner, air accumulated within thepilot hydraulic pressure chambers 40 and 41 is led to the drainpassageway 54 through the gaps at the respective threadedly engagingportions 52 and 53, and is released to the reservoir 6 through the drainline 34. In this connection, since the drain passageway 54 is providedindependently of the drain grooves 44 and 45 in the valve body section31, bleeding of air is effected excellently without being influenced bythe pressure of the hydraulic fluid in the grooves. This makes itpossible to effect air bleeding automatically without carrying outattaching and detaching of the adapters 48 and 49. Thus, no specialworking is required for the air bleeding, making it possible to reducethe maintenance cost.

Additionally, the inventors of this application ascertained thefollowing fact. That is, the pilot hydraulic fluid within the pilothydraulic pressure chambers 40 and 41 also flowed out into the drainpassageway 54 through the gaps at the respective threadedly engagingportions 52 and 53, depending upon the manufacturing accuracy of thethreads at the threadedly engaging portions 52 and 53. However, in caseof the hydraulic fluid high in viscosity as compared with air, anoutflow amount of the hydraulic fluid was extremely slight, for example,of the order of several tens cc/min. The amount of such order did notsubstantially influence usual moving action of the spools 37 and 38.

FIG. 5 shows a hydraulic pilot operated directional control valveaccording to another embodiment of the invention. In the figure, likereference numerals are used to designate component parts like thoseillustrated in FIG. 4. The hydraulic pilot operated directional controlvalve is generally designated by the reference numeral 60.

In this control valve 60, plugs 62 and 63 are provided in a hydraulicpilot operating section 61, in substitution for the adapters 48 and 49of the embodiment illustrated in FIG. 4. Like the adapters 48, 49, theplugs 62 and 63 are detachably mounted to a block 64 through respectivethreadedly engaging portions 52 and 53 which are formed respectively bythreaded engagement of male threads provided on the plugs 62 and 63 withfemale threads provided in the block 64. The embodiment is similar tothe first embodiment in that gaps at the respective threadedly engagingportions 52 and 53 constitute air-bleeding minute passageway means forbringing the pilot hydraulic pressure chambers 40 and 41 intocommunication with the drain passageway 54.

On the other hand, the block 64 is formed therein with pilot ports 65and 66 through which the pilot pressure is introduced into the pilothydraulic pressure chambers 40 and 41. The pilot port 66 is connected tothe pilot line 8, while the pilot port 65 is connected to a pilot linewhich is not shown.

Although not shown, the other hydraulic pilot operating section of thecontrol valve 60 is likewise constructed.

Like the above-mentioned first embodiment, it is possible also for theembodiment constructed in this manner to release air accumulated withinthe pilot hydraulic pressure chambers 40 and 41 from the gaps at therespective threadedly engaging portions 52 and 53 to the reservoir 6through the drain passageway 54 and the drain line 34, therebyautomatically carrying out air bleeding.

FIG. 6 shows a hydraulic pilot operated directional control valve 70according to still another embodiment of the invention. The controlvalve 70 also has a valve body section 71 and opposed hydraulic pilotoperating sections 72 (only one shown). However, the control valve 70 isso arranged as to offer a single control valve in which a single spool74 is accommodated in a block 73 of the valve body section 71, and asingle pilot hydraulic pressure chamber 76 is correspondingly formedwithin a block 75 of the hydraulic pilot operating section 72. The block73 of the valve body section 71 and the spool 74 are formed with variousgrooves including drain grooves 77 and 78. A spring 79 is accommodatedin the pilot hydraulic pressure chamber 76. An adapter 81 offering apilot port 80 is mounted to the block 75 of the operating section 72, sothat the pilot pressure is introduced from the pilot line 8 into thepilot hydraulic pressure chamber 76 through the pilot port 80.

A drain passageway 82 is formed in the vicinity of the pilot hydraulicpressure chamber 76 within the block 75. Like the above-mentionedembodiment, the drain passageway 82 is connected to the reservoir 6through the drain line 34. Formed between the pilot hydraulic pressurechamber 76 and the drain passageway 82 is a fine bore 83 serving asminute passageway means for bleeding air The fine bore 83 has across-sectional flow passage area of the order that enables passage ofair, but almost prevents passage of the pilot hydraulic fluid.

It is possible also for the embodiment constructed in this manner torelease air accumulated within the pilot hydraulic pressure chamber 76to the reservoir 6 through the fine bore 83, the drain passageway 82 andthe drain line 34, thereby likewise carrying out air bleedingautomatically.

As will be clear from the foregoing, according to the hydraulic pilotoperated directional control valve of the invention, release of airaccumulated within the pilot hydraulic pressure chamber or chambers tothe outside can be effected automatically. Thus, the manual operationrequired for air bleeding of this kind, which has conventionally beencarried out, can be dispensed with, thereby making it possible to reducethe maintenance cost involved in this operation.

What is claimed is:
 1. A hydraulic pilot operated directional controlvalve comprising:at least one pilot hydraulic pressure chamber formedwithin a block of a hydraulic pilot operating section of the valve, adrain passageway provided in the vicinity of said pilot hydraulicpressure chamber within said block, an adapter for connecting a pilotline to said pilot hydraulic pressure chamber, said adapter beingthreadedly attached on said block, and an air bleeding means forbleeding air in said pilot hydraulic pressure chamber to said drainpassageway, said air bleeding means including a gap formed in athreadedly engaging portion of said adapter and block extending betweensaid pilot hydraulic pressure chamber and drain passageway.